Basically, start with an introduction telling which areas of debate you'll discuss, some general comment about reinterpretation and, if the question includes a quotation, link to it.
Then go into discussing your areas of debate, the question will probably ask for two. It is important to discuss them historiographically, ie. don't spend ages narrating all the events of the Cuban Missile Crisis, etc., because the important part is the differing interpretations of the event by the various historians. I'd probably introduce the area of debate and then go through the different interpretations, starting from Sorensen/Schlesinger --> Reeves --> Hersh, or basically chronologically.
It is important to get across the context of each of your historians (ie. why they hold the views they do), you could do this either in a slab before you begin discussing the areas of debate or integrated throughout the essay, which is probably better.
Anyway perhaps the best way is to view exemplar samples, they are hosted
here or more specifically (Hist Ext. from 2002 HSC),
here.
